Add support for configuring the maximum DMA segment size. The maximum DMA segment size may be set to a value smaller than the virtual memory page size. No checks are performed on the new max_segment_size parameter because all positive values are valid. The value 0 is converted into a valid value by blk_validate_limits(). Since rq_for_each_segment() may yield bvecs larger than the maximum DMA segment size, add code in the rq_for_each_segment() loop that restricts the bvec length to the maximum DMA segment size. Cc: Christoph Hellwig Cc: Ming Lei Cc: Damien Le Moal Cc: Chaitanya Kulkarni Signed-off-by: Bart Van Assche --- drivers/block/null_blk/main.c | 13 +++++++++++++ drivers/block/null_blk/null_blk.h | 1 + 2 files changed, 14 insertions(+) diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c index 677ac829ef80..c43d74cdfd23 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -169,6 +169,10 @@ static int g_max_sectors; module_param_named(max_sectors, g_max_sectors, int, 0444); MODULE_PARM_DESC(max_sectors, "Maximum size of a command (in 512B sectors)"); +static unsigned int g_max_segment_size = BLK_MAX_SEGMENT_SIZE; +module_param_named(max_segment_size, g_max_segment_size, int, 0444); +MODULE_PARM_DESC(max_segment_size, "Maximum size of a DMA segment in bytes"); + static unsigned int nr_devices = 1; module_param(nr_devices, uint, 0444); MODULE_PARM_DESC(nr_devices, "Number of devices to register"); @@ -450,6 +454,7 @@ NULLB_DEVICE_ATTR(home_node, uint, NULL); NULLB_DEVICE_ATTR(queue_mode, uint, NULL); NULLB_DEVICE_ATTR(blocksize, uint, NULL); NULLB_DEVICE_ATTR(max_sectors, uint, NULL); +NULLB_DEVICE_ATTR(max_segment_size, uint, NULL); NULLB_DEVICE_ATTR(irqmode, uint, NULL); NULLB_DEVICE_ATTR(hw_queue_depth, uint, NULL); NULLB_DEVICE_ATTR(index, uint, NULL); @@ -608,6 +613,7 @@ static struct configfs_attribute *nullb_device_attrs[] = { &nullb_device_attr_index, &nullb_device_attr_irqmode, &nullb_device_attr_max_sectors, + &nullb_device_attr_max_segment_size, &nullb_device_attr_mbps, &nullb_device_attr_memory_backed, &nullb_device_attr_no_sched, @@ -805,6 +811,7 @@ static struct nullb_device *null_alloc_dev(void) dev->queue_mode = g_queue_mode; dev->blocksize = g_bs; dev->max_sectors = g_max_sectors; + dev->max_segment_size = g_max_segment_size; dev->irqmode = g_irqmode; dev->hw_queue_depth = g_hw_queue_depth; dev->blocking = g_blocking; @@ -1251,6 +1258,9 @@ static blk_status_t null_transfer(struct nullb *nullb, struct page *page, unsigned int valid_len = len; void *p; + WARN_ONCE(len > dev->max_segment_size, "%u > %u\n", len, + dev->max_segment_size); + p = kmap_local_page(page) + off; if (!is_write) { if (dev->zoned) { @@ -1298,6 +1308,8 @@ static blk_status_t null_handle_data_transfer(struct nullb_cmd *cmd, spin_lock_irq(&nullb->lock); rq_for_each_segment(bvec, rq, iter) { len = bvec.bv_len; + len = min(bvec.bv_len, nullb->dev->max_segment_size); + bvec.bv_len = len; if (transferred_bytes + len > max_bytes) len = max_bytes - transferred_bytes; err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset, @@ -1961,6 +1973,7 @@ static int null_add_dev(struct nullb_device *dev) .logical_block_size = dev->blocksize, .physical_block_size = dev->blocksize, .max_hw_sectors = dev->max_sectors, + .max_segment_size = dev->max_segment_size, .dma_alignment = 1, }; diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h index 6c4c4bbe7dad..43dc47789718 100644 --- a/drivers/block/null_blk/null_blk.h +++ b/drivers/block/null_blk/null_blk.h @@ -93,6 +93,7 @@ struct nullb_device { unsigned int queue_mode; /* block interface */ unsigned int blocksize; /* block size */ unsigned int max_sectors; /* Max sectors per command */ + unsigned int max_segment_size; /* Max size of a single DMA segment. */ unsigned int irqmode; /* IRQ completion handler */ unsigned int hw_queue_depth; /* queue depth */ unsigned int index; /* index of the disk, only valid with a disk */